Quartzite (Ferruginous)

Physical Properties

Hardness: 7 (Mohs scale), Color: Tan to reddish-brown due to iron staining, Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Formation & Geological History

Formed from the metamorphism of quartz sandstone under high heat and pressure, where quartz grains recrystallize into a locked mosaic. Found in ancient mountain belts and cratons.

Uses & Applications

Used in construction for road ballast, floor tiles, and as a decorative stone. In industry, high-purity varieties are used to produce silica sand for glassmaking and silicon for electronics.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rocks during weathering, forming prominent ridges and peaks in mountain ranges. It is harder than a steel knife and will easily scratch glass.

Field Identification & Locations

Identify by its extreme hardness and sugary, crystalline texture on a fresh break. Unlike sandstone, quartzite breaks through the quartz grains rather than around them. Found globally in metamorphic terranes.

Identified on: 5/3/2026

Mode: Standard